A lead frame provides a possibility to assure electrical connections between a semiconductor chip and the outside of a package which houses the semiconductor chip or die. A lead frame generally includes a die pad and a plurality of lead fingers.
A semiconductor die or chip is attached to the die pad and electrical connections between contact pads on the die and inner portions of the lead fingers are provided, for example by bond wires. After the electrical connection, a package may be formed, e.g. by molding a housing in a molding process. The housing encapsulates the die. An outer portion of the lead fingers extends out of the housing. The outer portion of the lead finger includes an attach portion which may be soldered to an external circuit such as a printed circuit board.
The attach portion of a lead finger should allow for a secure solder connection between the semiconductor package and the external circuit withstanding multiple temperature cycles.
Due to differences in the coefficients of thermal expansion of the semiconductor package and the external circuit to which the semiconductor package is soldered, cracks may arise in the solder joint leading to an increased resistance or even to an electrical disconnection between semiconductor package and external circuit.